What is the difference between HashMap, TreeMap, and LinkedHashMap?
HashMap vs TreeMap vs LinkedHashMap
In Java, HashMap, TreeMap, and LinkedHashMap provide different ordering and performance characteristics. HashMap is optimized for general key-value lookup, TreeMap maintains keys in sorted order using a tree, and LinkedHashMap maintains a predictable iteration order using a linked ordering structure in addition to hashing.
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HashMap: expected O(1) get/put; no general sorted iteration guarantee.
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LinkedHashMap: expected O(1) get/put; maintains insertion order, and can also be configured for access order.
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TreeMap: O(log n) get/put/remove; maintains keys in sorted order.
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HashMap is usually preferred for pure key-based lookup.
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TreeMap is appropriate for range queries, sorted traversal, and predecessor/successor operations.
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LinkedHashMap is useful when deterministic iteration order is required.
Follow-up Questions
- How does LinkedHashMap maintain insertion order?
- When would you choose TreeMap?
- What are the memory trade-offs?